# std::asctime

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< cpp‎ | chrono‎ | c

Defined in header `<ctime>` |  |
char* asctime( const std::tm* time_ptr ); |  |

Converts given calendar time std::tm to a textual representation of the following fixed 25-character form: Www Mmm dd hh:mm:ss yyyy\n.

- `Www` - three-letter English abbreviated day of the week from time_ptr->tm_wday, one of `Mon`, `Tue`, `Wed`, `Thu`, `Fri`, `Sat`, `Sun`.
- `Mmm` - three-letter English abbreviated month name from time_ptr->tm_mon, one of `Jan`, `Feb`, `Mar`, `Apr`, `May`, `Jun`, `Jul`, `Aug`, `Sep`, `Oct`, `Nov`, `Dec`.
- `dd` - 2-digit day of the month from timeptr->tm_mday as if printed by sprintf using %2d.
- `hh` - 2-digit hour from timeptr->tm_hour as if printed by sprintf using %.2d.
- `mm` - 2-digit minute from timeptr->tm_min as if printed by sprintf using %.2d.
- `ss` - 2-digit second from timeptr->tm_sec as if printed by sprintf using %.2d.
- `yyyy` - 4-digit year from timeptr->tm_year + 1900 as if printed by sprintf using %4d.

The behavior is undefined if any member of *time_ptr is outside its normal range.

The behavior is undefined if the calendar year indicated by time_ptr->tm_year has more than 4 digits or is less than the year 1000.

The function does not support localization, and the newline character cannot be removed.

The function modifies static storage and is not thread-safe.

### Parameters

time_ptr | - | pointer to a std::tm object specifying the time to print

### Return value

Pointer to a static null-terminated character string holding the textual representation of date and time. The string may be shared between `std::asctime` and std::ctime, and may be overwritten on each invocation of any of those functions.

### Notes

This function returns a pointer to static data and is not thread-safe. POSIX marks this function obsolete and recommends locale-dependent std::strftime instead. In std::locale`("C")` the std::strftime format string "%c\n" will be an exact match to `std::asctime` output, while in other locales the format string "%a %b %e %H:%M:%S %Y\n" will be a potentially closer but not always exact match.

POSIX limits undefined behaviors only to the cases when the output string would be longer than 25 characters, when `timeptr->tm_wday` or `timeptr->tm_mon` are not within the expected ranges, or when `timeptr->tm_year` exceeds INT_MAX-1990.

Some implementations handle timeptr->tm_mday == 0 as meaning the last day of the preceding month.

### Example

Run this code

    #include <ctime>
    #include <iomanip>
    #include <iostream>

    int main()
    {
        const std::time_t now = std::time(nullptr);

        for (const char* localeName : {"C", "en_US.utf8", "de_DE.utf8", "ja_JP.utf8"})
        {
            std::cout << "locale " << localeName << ":\n" << std::left;
            std::locale::global(std::locale(localeName));

            std::cout << std::setw(40) << "    asctime" << std::asctime(std::localtime(&now));

            // strftime output for comparison:
            char buf[64];
            if (strftime(buf, sizeof buf, "%c\n", std::localtime(&now)))
                std::cout << std::setw(40) << "    strftime %c" << buf;

            if (strftime(buf, sizeof buf, "%a %b %e %H:%M:%S %Y\n", std::localtime(&now)))
                std::cout << std::setw(40) << "    strftime %a %b %e %H:%M:%S %Y" << buf;

            std::cout << '\n';
        }
    }

Possible output:

    locale C:
        asctime                             Wed Nov  4 00:45:01 2020
        strftime %c                         Wed Nov  4 00:45:01 2020
        strftime %a %b %e %H:%M:%S %Y       Wed Nov  4 00:45:01 2020

    locale en_US.utf8:
        asctime                             Wed Nov  4 00:45:01 2020
        strftime %c                         Wed 04 Nov 2020 12:45:01 AM UTC
        strftime %a %b %e %H:%M:%S %Y       Wed Nov  4 00:45:01 2020

    locale de_DE.utf8:
        asctime                             Wed Nov  4 00:45:01 2020
        strftime %c                         Mi 04 Nov 2020 00:45:01 UTC
        strftime %a %b %e %H:%M:%S %Y       Mi Nov  4 00:45:01 2020

    locale ja_JP.utf8:
        asctime                             Wed Nov  4 00:45:01 2020
        strftime %c                         2020年11月04日 00時45分01秒
        strftime %a %b %e %H:%M:%S %Y       水 11月  4 00:45:01 2020

### See also

ctime | converts a std::time_t object to a textual representation (function)
strftime | converts a std::tm object to custom textual representation (function)
put_time (C++11) | formats and outputs a date/time value according to the specified format (function template)
C documentation for asctime

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